The present disclosure is related generally to bearings for supporting rollers in rolling mill applications, and in particular to a system and method for mounting roller support bearings.
Two types of bearings find widespread use in such rolling mill machinery, those being the tapered roller bearing and the cylindrical roller bearing, each of which is capable of carrying heavy radial loads. Tapered roller bearings lend themselves to adjustment in that the axial positions of the supporting races relative to each other control the radial clearance or play, and may even eliminate the radial clearance altogether. This in turn provides control of the size of the load zone, that is the number of rollers in the bearing which are actually under load at any instant. Notwithstanding this capability, tapered roller bearings, when used to transmit extremely heavy loads such as in rolling mills, are usually manufactured with their tapered rollers arranged in four rows, and with the tapers of adjacent rows oriented oppositely. This makes adjustments in the field difficult, and for all practical purposes these multi-row bearings are adjusted at the factory through the selection of spacers. There the bearings are usually set with a slight amount of axial clearance. However, the profile of the raceway on the cone or inner race is not perfectly circular nor is its axis perfectly coincident with the axis of rotation. These imperfections cause runout.
Cylindrical roller bearings, on the other hand, cannot be adjusted, and since some radial clearance must exist between the rollers and the raceways in order to assemble the bearings, cylindrical roller bearings inherently will have runout, given that the inner race cannot be ground to a perfectly round condition. Despite the inherent runout, the use of cylindrical roller bearings in mill rolls affords easier control over the runout derived from the manufacturing tolerances. For example, the raceway of the inner race, once that race is installed on the roll neck, may be ground reasonably true with respect to the axis of the roll. Typically, the mill roll, with the inner races of its bearings in place, is placed between centers with the roll neck later supported on steady rests. The grinding eliminates much of the runout caused by manufacturing tolerances in the roll neck and race, and the expansion tolerance of the press fit. However, some runout will remain due primarily to imperfections in the grinding operation itself, for the inner race may have one or more lobes in its profile after grinding.
The option of grinding to eliminate runout has not been available for tapered roller bearings, primarily because their races are at different inclinations, and the inner races or cones have ribs, all of which interfere with the grinding operations. Furthermore, alteration of a radial dimension on a tapered raceway affects the axial dimensions in the bearing, and requires the use of additional spacers or shims to compensate for the change in the axial dimension.
If the bearings supporting a roll in a rolling mill are improperly set, various problems can ensue. For bearings which have too much endplay, there is an increased chance of roller skidding (i.e. low load zone) and lower bearing life (as the load zone decreases, the load per roller ratio increases, and bearing life decreases.) Conversely, for bearings set with too much preload, there is the risk of bearing burn-up, which is generally a catastrophic damage and cannot be easily repaired.
Accordingly, it would be advantageous to provide a method and apparatus to facilitate the proper mounting and setting of roller bearings such as those used to support back up rolls in rolling mill applications. It would be further advantageous to provide such a method and apparatus to achieve good control over the bearing settings from a cold state through steady-state operating conditions.